Project 2: Project Summary/Abstract This project sets out a new methodology (Spatio-temporal Pollutant Tracking) to assess the pathways by which pollutants are transported and transformed in the atmosphere, Our hypothesis is that we can apply Spatio- temporal Pollutant Tracking to improve estimates of potential exposures, and ultimate public health impacts, of hazardous environmental pollutants. Such information is critical for accurate risk assessment and the development of effective remediation policies, but is currently limited by uncertainties in atmospheric chemistry and transport. The atmosphere serves as an efficient medium for both the efficient transformation of pollutants (forming products that may be of higher or lower toxicity of the parent compound) and the rapid transport of pollutants (leading to large heterogeneities in their temporal and spatial distributions). This high reactivity and high variability of atmospheric pollutants is often not considered in exposure assessments, a critical gap that leads to substantial uncertainties in the ultimate environmental/health impact of a given chemical. In order to reduce such uncertainties, we will develop a range of new state-of-the-art tools to better quantify this chemical processing and transport: 1) development and deployment of sensors to measure the concentrations of key atmospheric species; 2) laboratory studies of atmospheric transformations pollutants in the atmosphere; and 3) modeling of contaminant chemistry and transport in order to predict pollutant concentrations and fate. These three approaches are highly complementary, with outputs from each informing the other two. Central to this project is the study of not only the chemistry and distributions of the originally- emitted compounds (?primary pollutants?), but also their multi-generation atmospheric transformation/degradation products (?secondary pollutants?), which in some cases may be more hazardous than the precursor compound. This project focuses initially on polycyclic aromatic hydrocarbons (PAHs), an important class of toxic compounds on which we have carried out preliminary studies, and which allow for the development of our methodology. Our methods will then be extended and applied to nitrosamines (e.g., N- Nitrosodimethylamine, NDMA) and similar compounds, and ultimately to other compounds of interest. The improved characterization of atmospheric levels of these species will inform studies in other environmental domains (e.g., water and sediments, Project 1), and the improved ability to estimate human exposures and identify new target pollutants will aid the ability of biomedical studies (e.g., Projects 3-5 of this MIT-SRP) to determine the ultimate health impact of such chemicals. Researchers will engage the public, specifically communities in the Mystic River Watershed and tribal communities in northern Maine, by discussing sources and fates of atmospheric pollutants, and introducing them to novel sensor techniques with cellphone-enabled sensors, enabling ?citizen science?. The overarching goal is the development and application of new and innovative measurement and modeling approaches for the policy-relevant assessment of toxic substances. 1